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Date May 2017 Marks available 1 Reference code 17M.3.HL.TZ2.3
Level Higher level Paper Paper 3 Time zone Time zone 2
Command term State Question number 3 Adapted from N/A

Question

The rate of transpiration can be measured using a data-logging pressure sensor connected to a plant cutting via a plastic tube. In an experiment, a control set-up was connected to the tube and placed in a well-lit room with normal humidity levels.

State the specific type of plant tissue that the plastic tube is meant to model. 

[1]
a.

Predict, with a reason, what will happen to the pressure in this tube as transpiration occurs.

[2]
b.

Outline how this control set-up could be modified to test the effect of either humidity or temperature on the rate of transpiration.

[2]
c.

Markscheme

xylem

a.

a. pressure will decrease 

b. water volume decreases «in tube» due to evaporation transpiration 

c. «cohesion/tension of water column» causes increase in air volume «thus air pressure decreases» OWTTE

b.

Alternative 1

humidity

a. outline of how independent variable is varied  
eg: cover experimental plant«s» with a plastic bag
OR
mist the experimental plant«s».

b. outline of control treatment  eg: control plant«s» is/are not covered/not misted.

c. control of other variable«s» eg: light is kept constant.

Alternative 2

temperature

d. outline of how independent variable is varied  eg: place set-up under/away from heat lamps at different distances.

e. outline of control treatment  eg: no heat lamp for control.

f. control of other variable«s» eg: use hygrometer to verify that heat lamp does not change humidity level.

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Additional higher level » Topic 9: Plant biology » 9.1 Transport in the xylem of plants
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Additional higher level » Topic 9: Plant biology
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